Glossary — Page 452, Lesson 702

I want to walk you through a set of glossary terms that are essential for understanding how your body and mind behave in the aviation environment. Let's start with the inner ear. The semicircular canals are organs inside your inner ear. They are set in three planes at right angles to each other — think of them as three rings, each one perpendicular to the other two. Their job is to detect angular acceleration, meaning any rotation or turning motion of your head. They do not sense constant speed or linear motion; they only tell your brain when you start or stop rotating. Next, skill is defined as an organized and coordinated pattern of activity. That pattern can be physical — like flying an aircraft — or social, linguistic, or intellectual. A skill is not just a random action; it is structured and practiced. Now, slips are a category of errors. The key point here is that a slip happens when your intent was correct — you knew what you wanted to do — but the execution did not satisfy that intent. You meant to do the right thing, but your body or fingers did something else. That is a slip. Let's talk about the somatosensory system. This is a network of pressure and position nerve receptors distributed throughout your entire body. They provide information — for example, on the orientation of the seat on which you sit. So when you feel the seat pressing against your back or your legs, that is your somatosensory system at work. It works together with the vestibular apparatus (which includes the semicircular canals we just covered) and your vision to enable you to maintain an image of your spatial orientation — that is, your sense of where you are in space relative to the ground and the aircraft. Two sleep-related terms: somnambulism is sleep walking, and somniloquism is talking in one's sleep. Both are disorders of sleep behaviour. Staggers is a term you will encounter with decompression sickness. When nitrogen bubbles form in the blood and affect the blood supply to the brain, the sufferer can lose some mental and body control functions. That unsteady, staggering effect is called the staggers. Moving to the ear again: the stapes, also called the stirrup, is the innermost bone of the ossicles — the three tiny bones in your middle ear that transmit sound vibrations. The stroboscopic effect is a flickering effect of light. In aviation, it is often caused by a propeller or, in the case of a helicopter, the rotor blade turning and cutting the sunlight. This can create a dangerous illusion where moving parts appear to slow down or stop. Stereopsis is your ability to judge depth visually. It works because near objects produce images on each retina that are more different from one another than distant objects. Your brain compares those two slightly different images to calculate depth. A stroke is a term used to describe the effects of a blockage of one of the arteries to the brain. That blockage disrupts blood flow and therefore oxygen supply to that part of the brain. The result is a failure in the brain's ability to control a particular part of the body. Depending on which site is affected, the results could be paralysis, loss of speech, or loss of control of facial expression. Subcutaneous is an adjective meaning below or under the skin. For example, a subcutaneous injection goes into the layer under the skin. The sympathetic nervous system — the glossary tells you to see Autonomic Nervous System. That is the branch of your nervous system that handles the fight-or-flight response. A synapse is the connection between two neurons. It is the tiny gap where one nerve cell communicates with the next. Syncope is fainting caused by a fall in blood pressure. When your blood pressure drops enough, your brain does not get enough blood, and you lose consciousness. Tidal volume is the volume of air inhaled and exhaled with each normal breath. It is not the maximum you can breathe in — just the amount you move in and out during relaxed, resting breathing. Time of Useful Consciousness, abbreviated TUC, is the amount of time an individual is able to perform useful flying duties in an environment of inadequate oxygen. This is a critical number for pilots — if your oxygen supply fails at altitude, you have only a limited time before you cannot function effectively. A thrombus is a clot of blood that can stop blood flow to any organ. If that blockage is in one of the coronary arteries, a heart attack can result. If it is in an artery to the brain, the result will be a stroke. Finally, the trachea is the main airway leading from the nose and mouth into the chest cavity. It is a cartilage-reinforced tube — those rings of cartilage keep it open so you can breathe. It divides into two bronchi, which deliver air to the left and right lungs. These are all foundational terms. Take them one at a time, and let me know if you want to go deeper into any of them. Otherwise, when you are ready, just say 'next' and we will move on.